It is common practice to provide pagers which emit an audible tone indicating that a particular recipient is to receive a message. Thereafter, the message is transmitted via voice communication to the recipient whether or not this recipient is ready to receive the message. As a result, the content of the message is sometimes lost when the recipient either cannot remember the content of the message or a pencil and paper is not immediately available to transcribe the message. This results in frustration of the recipient and the necessity of communicating with the originator of the message to obtain its content. In one broad aspect this invention alleviates the inconvenience of the prior art paging systems by providing storage and recall of the transmitted message through the use of a printed tape (hard copy unit).
As illustrated in U.S. Pat. No. 3,846,783 issued to Aspell et al. on Nov. 5, 1974, it is known to provide a pager with a hard copy printout utilizing a thermal print head. As discussed in this patent the thermal print head is advanced with the printing of each character. This presents a problem of synchronizing the print head advancement with the read out from the ASCII decoding logic. Not only must synchronization circuitry be supplied, but also the mechanical stability of the system must be such as to accommodate a moving print head or moving tape which is indexed with the printout of each character of the message. This not only requires complicated indexing of the print head relative to the printing medium, or vice versa, but also requires bulky drive apparatus which draws excessive current. As will be described, in accordance with one aspect of this invention, the subject invention utilizes a "printing-on-the-fly" technique which utilizes a fixed print head and a free running tape to eliminate the necessity of synchronism between the print head and the recording tape. This system obviously, therefore, eliminates the necessity of indexing.
Before describing the aspects of the "printing-on-the-fly" embodiment, it will be appreciated that with respect to the Aspell patent, the address decoding is digital and does not utilize a tone decoding system. In one embodiment, the subject invention utilizes a new type low current or power drain tone decoder which is normally-off rather than being normally-on, as is the case in the prior art. Moreover, in one embodiment, the FSK decoding in the subject invention only utilizes one of the two FSK tones while the Aspell et al. device is one which necessitates the detection and utilization of two tones.
Thus, the subject system incorporates a number of circuitry saving and battery saving components.
"Printing-on-the-fly" refers to the continuous movement of the printing medium past a print head without indexing the head with respect to the printing medium, or vice versa. While printing-on-the-fly has been accomplished before with thermal print heads as illustrated in U.S. Pat. No. 3,777,116 issued to Riccardo Brescia and Lucio Montanari, its adaptation to a hand held pager is unique. One of the reasons for the uniqueness of this application is the problem of power drain from the batteries by the tape drive itself. Where power is plentiful, printing-on-the-fly is not a problem because the tape drive speed may be made substantially constant. However, in a battery powered operation, especially when the batteries are small, such as in pagers, battery voltages vary widely. In the past, in battery powered tape drives extra circuitry has been utilized to stabilize the speed of the motor in view of the start-up voltage transient as well as variation in the battery voltage with constant high drain. This has been accomplished most notably in the pocket cassette-type tape recorders which utilize magnetic tapes and audio signals. However, the "printing-on-the-fly" technique as described herein obviates the necessity for complicated and, in some instance, excessive power-draining motor drive control circuits because it is a finding of this invention that the speed of the tape drive motor may vary by as much as 50% and still produce a readily readable message. Hence, there need be no indexing of the thermal print head with respect to the paper and, more importantly, there need be no special control of the speed of the tape drive motor. This lack of synchronism and lack of criticality has been discovered and lies at the heart of providing an exceptionally simple hard copy, long life pager. Message samples with various tape drive rates are illustrated hereinafter to illustrate the range of speeds acceptable and thus the lack of necessity of tape speed control.
"Printing-on-the-fly", therefore, eliminates the necessity for indexing equipment which eliminates reliability problems, cost and, in some instances, excessive power drain in battery powered units. The subject system is extremely reliable due to the lack of criticality between the tape movement and the printing speed.
Additionally, with respect to the hard copy pager, a hard copy unit is provided with a removable transparent cover. This cover provides a portion of a track for the tape which is imprinted while at the same time, because of its transparency, provides for viewing of the tape and the message thereon while the tape is within the hard copy unit. Thus, for short messages the tape need not be removed from the unit for viewing.
In one embodiment, FSK modulation is used for the transmission of the message. It will be appreciated that FSK transmission involves the use of two tones for the transmittal of data. In the prior art, two filters are normally provided at a remote receiver, one tuned to one of the tones while the other being tuned to the other of the tones. However, in the present system, one of the filter circuits can be eliminated. The elimination of one filter assumes that the absence of output from the single filter indicates the presence of the other tone. The present system thus provides a unique demodulator and filter system which permits the use of this simplified system for the receipt of FSK data with existing FSK techniques. It will be appreciated, however, that conventional two-tone FSK demodulation may also be used with this invention.
The two tones utilized for the FSK transmission are different from the addressing tones utilized in the two tone address embodiments of the subject invention. To provide for the recognition of the two addressing tones a unique logic circuit is provided to recognize the particular tones arriving in a predetermined sequence. This differs from the tone unlatching systems of the prior art in which the arrival and detection of the first tone unlocks the second tone detector. It will be appreciated that in the prior art systems, decoding is accomplished when there is an output signal from the second tone detector. In the present invention, input signals are simultaneously applied to two filters tuned to the different tones. The outputs of these filters are coupled to a logic circuit which responds only to the desired address sequence. This logic circuit also permits group calls in which a number of pagers are addressed simultaneously. The decoding section of the subject tone decode circuit takes on the form of timing circuits which are normally-inoperative and are rendered operative only during the presence of a particular tone. This saves considerable battery power and is unlike any prior art tone detection system which operates just exactly the reverse by having normally-on decoders. Moreover, shock protection is provided by an override circuit which inhibits the output from one timing circuit when the other tone is present. This prevents false addressing when the pager is, for instance, banged against the side of a desk. The reason for the shock protection is that the filters are tuning fork type filters which, if subjected to mechanical shock, as by the bumping of a pager, produce output signals. These signals may falsely indicate the predetermined address.
It is therefore an object of this invention to provide an improved hand held paging system in which a message transmitted to a recipient is stored at the pager for readout at the convenience of the recipient.
It is another object of this invention to provide a paging system which is both inexpensive and makes few demands on the portable power supply contained within the pager.
It is yet another object of this invention to provide a pager with a printing system in which there is continuous relative movement between the printing head and the printing medium without significant distortion of the printed characters.
It is a still further object of this invention to provide a method and apparatus for transmitting a message to a portable unit in which the message is stored and displayed for the convenience of the recipient of the message by serial recording of the message on a tape imprinted "on-the-fly".
It is yet another object of this invention to provide a method of transmitting a message in which the message is stored at a remote location in a memory and in which the message is recalled by the recipient at his convenience.
It is a still further object of this invention to provide an improved low drain tone decoding system in combination with a hard copy pager.
It is a further object of this invention to provide a novel group call system in combination with a hard copy pager.
It is yet another object of this invention to provide a hand held pager unit which involves the imprinting of a tape and the guiding of the imprinted tape by virtue of a removeable transparent cover which permits viewing of the imprinted tape without removal of the tape from the unit.
It is a yet still further object of this invention to provide a snap on receptacle for preventing tape jamming when the pager is placed adjacent objects which may block the tape exit.